dirham

The size of the dirham

Q: I want to know about impurity that is equal to one Dirham. As I am in Pakistan, so tell me the size of the coin here. I have searched a lot but I didn't understand clearly. So please tell me in simple words. Also, I am very disturbed due to semen. Bad thoughts come untimely and some liquid comes out, so that Dirham concept applies here? Because I pray five times a day, I can't take a bath again and again. Please help me.